------- Comment #1 from pinskia at gmail dot com 2009-12-30 13:14 -------
Subject: Re: New: wrong code with -O1
Sent from my iPhone
On Dec 30, 2009, at 7:56 AM, "debian-gcc at lists dot debian dot org"
<gcc-bugzi...@gcc.gnu.org
> wrote:
> current trunk/branches on x86_64-linux-gnu. return values with
> different
> compilers and different optimizations:
>
> -O0 -O1 -O2 -O3
> gcc-4.1 0 2 2 2
> gcc-4.3 0 2 2 2
> gcc-4.4 2 0 0 0
> gcc-4.5 0 1 0 0
>
> Matthias
>
> #include <stdbool.h>
> #include <stdio.h>
>
> static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long
> bit) {
> bool res;
>
> __asm__ __volatile__( "btr %2,%1\n"
> "adc $0,%0\n"
> :"=r"(res), "=m"(*v)
> :"r"(bit), "r"(0)) ;
> return res ? 1 : 0;
This inline-asm looks wrong. Because it says *v is always overriden.
So if that function is inlined, flags down below does not have to be
set before it.
> }
>
> int main(void)
> {
> unsigned long flags = 0;
> int j;
>
> j = atomic_test_and_reset_bit(&flags, 2);
>
> printf("%d\n", j);
>
> return 0;
> }
>
>
> --
> Summary: wrong code with -O1
> Product: gcc
> Version: 4.4.3
> Status: UNCONFIRMED
> Severity: normal
> Priority: P3
> Component: target
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: debian-gcc at lists dot debian dot org
> GCC target triplet: x86_64-linux-gnu
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553
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